Growth and reactivity of evaporated platinum films on Cu(111): a study by AES, RHEED and adsorption of carbon monoxide and xenon

Abstract

Ultra thin platinum films evaporated on Cu(111) at 100 K and at room temperature have been investigated by AES, RHEED, temperature programmed desorption (TPD) of carbon monoxide and photoemission of adsorbed xenon (PAX). A layer-by-layer growth mechanism was evidenced up to at least 5 ML Pt. In the first Pt monolayer, the PtPt bond distances are strained ∼7% beyond the equilibrium bond distances found for bulk platinum. CO TPD is very sensitive to the coverage of deposited Pt: during the first Pt monolayer built-up the disappearance of Cu adsorption sites is observed and new features related to platinum are observed; at monolayer coverage, it appears that molecular CO is more weakly bound than on bulk Pt, the maximum of the main desorption peak is lowered by about 120–150 K; a 2 ML Pt deposit gives rise to CO TPD spectra looking like CO TPD spectra of bulk platinum. The binding energy of the Xe5p 1 2 levels used in PAX experiments as a local probe for the work function shows that the surface properties during the built-up of the first monolayer of platinum remain close to those of Cu(111). Adsorption of xenon and of carbon monoxide on 1 ML Pt present behaviors very close to those observed on the surface of a bulk PtCu alloy. An interpretation in terms of strong modifications of the electronic structure due to PtCu interactions is proposed.